Generally conventional type of trip meters are of the mechanical type. In such trip meters a mechanical counter including a numeral display device is driven via reduction gears by a drive shaft operatively connected to the transmission or other mechanism of the vehicle. When the driver of the vehicle intends to measure a distance between two points he will drive between, the driver resets the trip meter to zero so that the trip meter will count over the distance travelled, from zero. The trip meter is used not only for merely measuring the travelled distance but also for estimating the remaining distance to a goal or an objective point when the driver is aware of the distance between the two points, i.e. the starting point and the objective point. In order to ascertain the remaining distance on the way to the objective point the driver, however, must subtract the actually travelled distance which is displayed from the known distance by mental calculation.
For eliminating the inconvenience of such mental calculations, a trip meter which displays the remaining distance is desirable. Such a trip meter can be easily imagined since it is possible to ascertain the remaining distance by reducing a preset distance (numerals) in an opposite manner thereby subtracting the actually travelled distance from a preset distance. Although this type of a trip meter is convenient while the actually travelled distance does not exceed the preset distance, it is troublesome for the driver to ascertain the actual distance travelled if the distance exceeds the distance preset in the meter since he must add the distance corresponding to the excess to the preset distance. Moreover, if the preset distance is radically different from the actually travelled distance, the vehicle driver may not be able to determine if the displayed distance indicates the remaining distance or the excess of the distance. Therefore, such a trip meter which displays only the remaining distance can not satisfy all of the present day drivers needs.
Further with either such a trip meter or the conventional trip meter a distance displayed either in the form of actually travelled one or the remaining one, does not represent a distance along a predetermined course if the vehicle has taken a wrong course. Assuming the vehicle takes a wrong course from a point along the predetermined course and returns to the point after the vehicle driver notices that he was on a wrong course, the distance along the wrong course is added to the distance displayed as the one travelled Therefore, the distance displayed does not correspond to the distance of the predetermined course. In order to ascertain only the distance along the predetermined course the vehicle driver has to subtract the distance travelled along the wrong course from the displayed distance.